1)If direct download link of tarball is not available then add some text in
comments on how tarball can be created?
2)for desktop file installation you should use desktop-file-install command.
see
http://fedoraproject.org/wiki/Packaging/Guidelines#head-d559ee7363418a5840ce63090c608c991cd39ce6
here, you may like to add --vendor="fedora"
3) rpmlint output on srpm gave me
system-summary.src: W: strange-permission system-summary.spec 0600
A file that you listed to include in your package has strange
permissions. Usually, a file should have 0644 permissions.

1) You are missing BuildRequires: python-devel
2) use --vendor="Fedora" like --vendor="fedora"
3) you added fedora tag to desktop file that mean your file name will be changed
from system-summary.desktop to fedora-system-summary.desktop
so correct it under %files section

(In reply to comment #7)
> When I rpmbuild above SPEC on F8 and installed it and tried to start it from
> console, I got
> fatal: unable to import system_summary
> No module named system_summary.main
>
> What should be problem?
Kind of odd. Is that just running 'system-summary'? I've had no problems on my
F8 machine